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Bear in mind that's the sort of list I had with the Merc and I never did solve the problem, but:
Things which get hot in traffic but not when moving - sort of rules out anything connected to engine temperature, as cooling system is working fine. Therefore, look at electrical components - switches, sensors, valves, connectors etc which live in the hotter parts of the engine - on an NA car that would be the exhaust side, but on a turbo it might be other places too.With wiring, older cars get brittle insulation which then flakes off. When wires get hot they might expand/soften and sag, and you get a short. Sometimes the wires themselves corrode inside the insulation (Italian cars are terrible for this) or sometimes connectors fail (old British cars usually). Could be anything, but wires to and from sensors, relays, etc.
Does underbonnet heat have anywhere to escape? Do you have vents in the bonnet or scuttle? Have you ceramic coated or wrapped the exhaust to keep the temps down?
To confirm the flooding, what are the spark plugs like? black and wet?
Then of course everything might be working perfectly and it's your fuel mapping. If it was a carb I'd be looking at jetting. EFI offers too many variables.
OBD2 port, nothing comes up on the Volvo tool.
Something is getting hot, I think, but what gets hot in traffic that doesn't get hot when being driven hard on track? Something that is in air-flow on track but isn't in traffic.
What is that thing?
failing fuel pump? Matt thinks it's flooding, not dying. I could not smell fuel today though.
clogged injectors? They are new, and work find when the cars "aired" for 10 mins
air leak or blockage? (do you have an idle air hose? do you have an oil overflow that goes back into the intake?) All the pipe work is new, PCV does go back into the intake, yes it has an IAC valve.
vacuum issues? What type of issue?
faulty wiring - how hot does it get under there? What wiring?
dizzy cap / HT leads / plugs / rotor arm / plug coils (delete as appropriate) All new a month ago.